A gas turbine engine for an aircraft, including the following:
a core engine including a turbine, a compressor, and a core shaft connecting the turbine to the compressor;
a fan, which is positioned upstream of the core engine, wherein the fan includes a plurality of fan blades; and
a gear box which can be driven by the core shaft, wherein the fan can be driven at a lower rotational speed than the core shaft by means of the gear box, wherein
the core shaft is designed as a drive shaft for the gear box and has at least one axial first region which has a diameter greater than the diameter of at least one axial second region, wherein the at least one first region is arranged axially between the drive side of the gear box and a mounting and/or attachment on a static part of the gas turbine engine.